1. Field of the Invention
This invention pertains to closed cycle hot gas engines operating on the Ericsson Cycle. Operation of the working gas inside either cylinder and working gas transfer between cylinders is effected by pistons, whose motion is controlled by specially shaped cams mounted on a commonly driven shaft. Alternatively, operation and transfer of the working gas in another embodiment are controlled by valving members that are liquid piston level synchronized to operate with expansion and compression steps of the Ericsson cycle. In all the embodiments of the invention isobaric working gas transfer form one cylinder to the other in between the isothermal expansion and compression steps is insured by having the heating and cooling cylinder volumes in the same ratio as the absolute temperature of their respective isothermal processes.
In order to discuss the invention engine it is necessary first to consider prior state of the art hot gas engine development. Hot gas engines operating on either the Stirling (isochoric) or Ericsson (isobaric) cycles, with heat regeneration, are potentially capable of achieving Carnot efficiency, i.e., the maximum thermal efficiency achievable. This promise of maximized fuel economy, combined with broadening of heat sources that can be utilized in these engines and the relatively pollution free operation, as compared with Otto and Diesel internal combustion engines has resulted in much work being done on embodiments which attempt to mechanize the Stirling and Ericsson cycles. Both literature as well as various patents abound with examples including: PA1 ensuring that virtually all of the working gas is contained within the heating cylinder during expansion; PA1 ensuring that virtually all of the working gas is contained within the cooling cylinder during compression; PA1 ensuring that isobaric working gas transfer between the paired cylinders is optimized by providing a working gas volume in the heating cylinder which is greater than the corresponding volume in the cooling cylinder, the volume ratio being in the same ratio as the absolute temperatures of their respective isothermal processes; PA1 ensuring that isobaric working gas transfer between the paired cylinders is optimized by making the ratio of the rate of decrease of gas volume in the sending cylinder to the rate of increase of gas volume in the receiving cylinder equal to the ratio of the absolute temperature of their respective isothermal processes.
Rhythmic expansion and compression of working fluid hot gas engine foreign patents issued to N. V. Phillips, "Hot Gas Engines and Refrigeration Engines and Heat Pumps Operating on the Reversed Hot Gas Engine Principle," British Pat. No. 694, 856, dated 29 July 1953, and "Thermodynamic Reciprocating Machine," British Pat. No. 1,064,733, dated 5 Apr. 1967. Various other U.S. Patents including; W. A. Ross, "Stirling Engine Processes," U.S. Pat. No. 3,845, 624, dated 5 Nov. 1972, J. Koenig, "Hot-Air Engine," U.S. Pat. No. 1,614,962, dated 18 Jan. 1927, D. A. Kelly, "Composite Thermal Transfer System for Closed Cycle Engines." U.S. Pat. No. 3,635,017, dated 18 Jan. 1972 and "Uniflow Stirling Engine and Frictional Heating System," U.S. Pat. No. 3,579,980, dated 25 May 1971, C. G. Redshaw, "Rotary Stirling Engine," U.S. Pat. No. 3,984, 981, dated 12 Oct. 1976, M. Shuman, "Double Piston Engine," U.S. Pat. No. 3,583,155, dated 8 June 1971 and "Oscillating Piston Apparatus," U.S. Pat. No. 3,807,904, dated 18 Feb. 1974 and continuation U.S. Pat. No. 3,899,888, dated 19 Aug. 1975, G. A. P. Andman, et al, "Hot-Gas Reciprocating Engine," Netherlands Pat. No. 7,212,380, dated 13 Sept. 1972 and U.S. Pat. No. 3,854,290, dated 17 Dec. 1973, J. Cloup, "Isothermal Chamber and Heat Engines Constructed Using Said Chamber," France Pat. No. 7,804,308, dated 15 Feb. 1978 and U.S. Pat. No. 4,285,197, dated 25 Aug. 1981, A. A. Keller, et al, "Reciprocating Piston Engine Specifically Hot Gas Engine or Compression," Federal Republic of Germany Pat. No. 2,736,472, dated 12 Aug. 1977 and U.S. Pat. No. 4,271,669, dated 9 June 1981. PA0 Finally no citing of Stirling Cycle hot gas engine development could be complete without listing the 500 plus page work "Stirling Engines" written by Graham Walker and published by Oxford University Press, 1980.
In the majority of hot gas engine embodiments heating and cooling of the working gas takes place outside the cylinders. Thus, the working gas contained in the volumes swept by the power pistons does not get properly heated during expansion nor properly cooled during compression. Hence, the actual cycle in these embodiments is different from either the Stirling or Ericsson engine cycles and they cannot achieve Carnot efficiency.
There are improved hot gas engines where the heating and cooling regions are incorporated within the cylinder volumes swept by the power pistons. However the piston motion in these engine embodiments is continuous. The continuous piston motion causes portions of the working gas to continuously cross over from the heating cylinder to the cooling cylinder while gas expansion is in progress. The fraction of the gas that crosses over is a function of the compression ratio and increases as the compression ratio is increased. A similar crossover takes place between the heating and cooling cylinders during the gas compression step. It can be shown that the gas present in the cooling cylinder during each instant the expansion is in progress and the gas present in the heating cylinder during each instant the compression is in progress produce negative work cycles that reduce the thermal efficiency of the engine from the Carnot efficiency.
It is therefore desirable to provide a hot-gas engine in which its operating cycle thermal efficiency is maximized by:
The thermal efficiency of the invention hot-gas Ericsson cycle engine, disclosed herein, is maximized by incorporating means to accomplish the above requirements.